Fisher MC-620 - Page 2

CAUTION ON RF ADJUSTMENT
This model uses a microprocessor for memory preset contro! for the various bands.
This function has been used to preset frequency points for the different bands to permit adjustment and make it
possible to check the function of the microprocessor. To use this supplemental function, ground initialize test point
TP601 for 1 second before beginning adjustment. The following table shows the initially preset frequencies.
2 5 | 6
108MHz 98MHz
1629kHz 1404kHz
87.5MHz
522kHz
AM TUNER ALIGNMENT
AM ALIGNMENT — Band Selector switch to AM position.
Maintain generator output as low as possible for suitable indication.
Note: Perform this alignment after FM Tuner Alignment.
ITEM GENERATOR DIAL SETTING INDICATOR
1. AMIF Connect 450kHz Radio Position of Connect Radio IF Adjust AM IFT (L107) for maximum
ALIGNMENT IF Genescope output to non-interference Genescope input gain and best symmetry.
TP2 and ground. Minimum to TP4 and ground | Keep signal! low enough for noise
Adjust output level Frequency. lead to chassis. on response.
to 90dBuV.
2. AM RF Do not connect Set Preset Connect DC Volt- | Check DC Voitmeter for Indication
FREQUENCY generaior. STATION button meter to TP9 and 0.8V ~ 1.4V.
COVER H to “1” position. ground lead to
ALIGNMENT Set to 522kHz. chassis.
(522kHz)
Check DC Vo!tmeter for indication
7.0V ~ 9.0V.
Same as above. Change Preset Same as above.
STATION button
to “2” position.
Set to 1629kHz.
Then, confirm that each voltage becomes 1.0V tc 7.9V at receiving frequency
(1629kHz}
Note: Repeat the adjustments in Items 2 and 3.
of 522kHz to 1629kHz. (See Table 1)
i 4. AM RF Connecti Standard Loop T Set Preset Connect DC Volt- Adjust AM Antenna Coil (L108) for
TRACKING Antenna to output STATION button meter to TP8 maximum gain output.
ALIGNMENT terminal of AM RF Signal | to “3” position. and ground lead
(603kHz} Generator. Place Loop Set to 603kHz. to chassis.
Antenna 60cm away from
Loop Antenna (Unit).
5. Generator Setting to
(1404kHz) 603kHz or 1404kHz.
Modulate with 400Hz to “4” position.
| (30 % modulation). Ip Set to 1404kHz.
Note: Repeat the adjustments in Items 4 and 5. Then, confirm there is no tracking error.
Change Preset Same as above.
STATION button
Adjust AM Antenna Trimmer (TC103)
for maximum gain output.
6. AM AUTO Change Signal Set Preset Front Panel Adjust VR602 until the TUNED
STOP Generator setting STATION button TUNED Indicator Indicator partly light up.
SENSITIVITY to 999kHz. to “5” position. Display.
ADJUSTMENT | Adjust attenuator Set to 999kHz.
output for 60dBuV/m.
Use a screwdriver with plastic grip for all adjustments.
AM Frequency Cover Range
Tuning Voitage Value at TP405
(Table 1)
| | 522kKHz | 1629kKHz
Typical 1.0V 7.7NV
FM Frequency Cover Range
Tuning Voltage Value at TP405
(Table 2)
ete fs 87.5MHz | 108MHz
[Riaximum | rev_[ soy